Procedures for deriving equation of state mixing rules based on matchi
ng the zero pressure excess Gibbs energy to that of a previously param
eterized activity coefficient model are discussed. I have investigated
the conditions required for accurate reproduction of the original mod
el and provide a simple graphical tool for evaluating the error of the
equation of state mixing rule. An extension of the MHV-2 mixing rule
to incorporate mixtures containing components with very low volatility
is suggested.